This invention relates to a bonded structure that provides high adhesion strength and containment of interfacial impurity diffusion and methods of manufacturing the same.
Bonding of multiple substrates is required to enable three-dimensional integration of chips. Bonding of two substrates can be effected by adhesion between two dielectric materials as in an oxide-to-oxide bonding that fuses silicon dioxide materials from two substrates after bonding, by adhesion between two metallic material as in a copper-to-copper bonding that employs direct contact between two copper pads and a subsequent grain growth across the original interface between the two copper pads, or by a method employing a combination of the two adhesion mechanisms.
Through-substrate-via (TSV) structures, formed after multiple substrates are bonded and optionally thinned, provide electrical connection across the multiple substrates in a bonded structure. A TSV structure includes a conductive material such as copper, which diffuses rapidly in the plane of the bonding interface between substrates because microscopic irregularities and cavities are present at the interface. Diffusion of the conductive material from a TSV structure can cause electrical shorts and reliability problems in the bonded structure. This can be caused by a misalignment during the bonding of the substrates.
An interface between diffusion resistant materials, such as silicon nitride, across bonded substrates can be employed to reduce later diffusion of conductive material from TSV structures. In this case, the diffusion resistant materials retard lateral diffusion of the conductive material from the TSV structures along the interface between two bonded substrates, thereby preventing electrical shorts. Adhesion between the substrates is provided by forming a metal-to-metal contact between metal pads that are embedded in the diffusion resistant materials of both substrates. In this structure, areas including TSV structures have an interface between two diffusion resistant materials of the two substrates. Such an interface between two diffusion resistant materials of the two substrates does not provide significant adhesion strength between the two substrates. The adhesion strength between the two substrates is mostly provided by the metal-to-metal contact between the metal pads that are embedded in the diffusion resistant materials. To provide sufficient adhesion strength between the two substrates in this type of structure, the area for the metal pads must be sufficiently large and the area for formation of TSV structures must be limited. This constraint also limits the number and/or size of the TSV structures and the capacity to transmit power and electrical signals across the bonded substrates. In addition to the diffusion resistant material and the metal across the substrates, there are areas of silicon oxide which will line up to the corresponding substrate for an oxide to oxide bond surface in conjunction with the metal to metal bonding.